Clays and Clay Minerals, Vol. 58, No. 4, 532–541, 2010.
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Authors
Holmboe, Michael
Wold, Susanna
Jonsson, Mats
Issue Date
2010
Type
Article
Language
Keywords
Periodicals , Geology , Colloid Filtration , Compacted Bentonite , Gold Colloids , Diffusion , Microstructure , Nuclear Waste Disposal
Alternative Title
Colloid Diffusion In Compacted Bentonite: Microstructural Constraints
Abstract
In Sweden and in many other countries, a bentonite barrier will be used in the repository for spent nuclear fuel. In the event of canister failure, colloidal diffusion is a potential, but scarcely studied mechanism of radionuclide migration through the bentonite barrier. Column and in situ experiments are vital in understanding colloid diffusion and in providing information about the microstructure of compacted bentonite and identifying cut-off limits for colloid filtration. This study examined diffusion of negatively charged 2-, 5-, and 15-nm gold colloids in 4-month diffusion experiments using MX-80 Wyoming bentonite compacted to dry densities of 0.6-2.0 g/cm3. Breakthrough of gold colloids was not observed in any of the three diffusion experiments. In a gold-concentration profile analysis, colloid diffusion was only observed for the smallest gold colloids at the lowest dry density used (estimated apparent diffusivity Da&5610-13 m2/s). The results from a microstructure investigation using low-angle X-ray diffraction suggest that at the lowest dry density used, interlayer transport of the smallest colloids cannot be ruled out as a potential diffusion pathway, in addition to the expected interparticle transport. In all other cases, with either greater dry densities or larger gold colloids, compacted bentonite will effectively prevent diffusion of negatively charged colloids due to filtration.
Description
gsccm58408-hol.pdf -- 373KB
Citation
Clays and Clay Minerals, Vol. 58, No. 4, 532–541, 2010.
Publisher
The Clay Minerals Society
License
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